To fix your site immediately, please remove P3 by removing or renaming the following files and folders via FTP:

wp-content/plugins/p3-profiler (the whole folder)

wp-content/mu-plugins/p3-profiler.php (if it exists)

Your site was probably running very close to the 32M memory limit you had set. When you activated P3, it pushed it just over the limit and this error happened. Removing P3 should fix the error right now. For the long term, consider raising the memory limit.